A standard bale-tying unit of the Deering type that forms a knot in the tie, which can be either a metal wire, a filament twine, or even a synthetic-resin filament, has tie-holding disks rotatable about a horizontal axis adjacent the trailing bale end and a knotter rotatable about a vertical axis upstream of this trailing bale end. After each tying operation the free end of the tie is left in this holder and this tie extends downstream over the leading end of the bale and then back along underneath it. At the trailing bale end the tie passes through a needle which can engage up behind the bale when the plunger of the baling machine has compressed it downstream. When the needle does this it engages a portion of the tie in the holder, which rotates as the needle withdraws so that the tie is very tightly held around the bale.
The knotter is provided immediately adjacent this holder and has, relative to its vertical axis lying generally at the trailing bale end, upper and lower radially extending jaws, the lower of which is fixed and the upper of which is shaped like a hook and pivotal toward and away from the lower jaw. The knotter first rotates with the two jaws together to loop the two strands of the tie around itself, but on returning opens its two jaws so the strands are caught between them. This leaves a complete loop of both strands of the tie wound around the two jaws with the two ends then passing between these jaws. The ties are then cut between the knotter and the holder and the loop is pushed off the knotter, releasing the double overhand knot thus formed. This effectively and neatly knots the ends of the portion of tie snugged around the bale. The entire operation is wholly automatic, very fast, and quite smooth. Simple cams acting on the needle, holder, knotter, and knife displace these elements wholly pivotally for perfectly synchronous operation.
The jaws are usually tapered toward their tips, that is away from the knotter pivot axis. The stripper usually is formed with a notch that conforms to the shape of the upright lateral sides and the lower side of the lower jaw at its widest dimension. Thus as the stripper pivots or slides along the knotter to strip the loops of the tie from it, the space between the edges of the stripper at the notch and the corresponding sides of the lower jaw increases.
When a relatively thin tie is used, as for example a tough synthetic-resin cord, it is possible for this tie, which is under some tension as the plunger of the baler releases the hay or other crop contained by it, to slip between the stripper and knotter and remain caught on the knotter. The bale thus hangs up on the knotter. If the machine is not set up to shut down in this case, it can be damaged seriously as the conveyor attempts to pull out the old bale so a new bale can be formed.
West German patent document No. 1,164,922 and East German utility model 9341 of G. Raussendorf describe an arrangement wherein friction between the loops on the jaws is minimized by forming the lateral sides of the lower jaw with oppositely outwardly open grooves. This minimizes the contact area between the tie and the knotter to make it easier to push it off the knotter. Nonetheless for safety's sake it is standard practice even with this system and a small-section tie to use low tension to prevent the equipment from jamming, thereby creating undesirably loose bales.